The invention relates to a safety device for preventing the discharge of fuel from the fuel system of internal combustion engines.
In modern internal combustion engines which use electromagnetic injection valves only a fuel supply line which is under system pressure is needed for supplying fuel from the fuel tank to the engine. As a result, there is no need for the fuel rail system normally used and also a return line. Also, the heating of the fuel which occurs when it passes through the engine is avoided. In the new systems, a shortened return flow line, which no longer extends through the engine can therefore be used as it is described, for example, in DE 44 25 252 A1.
In these systems, the system pressure is controlled by a pressure controller which is integrated in the fuel filter. Such a pressure controller is known, for example, from DE 43 12 857 A2 or DE 43 02 382 A1. It has a spring chamber which needs to be vented to the atmosphere because pressure fluctuations would occur due to changes in altitude or temperature. Provided in the pressure controller is a diaphragm which is deflected due to a build-up of pressure and thus compresses a spring in the spring chamber, as a result of which the pressure control is ultimately effected. At the same time, the diaphragm prevents the fuel in the fuel-air mixture flowing through the pressure controller from escaping into the atmosphere.
The diaphragm is, however, insufficient as a safe-guard against the escape of fuel into the atmosphere since it could break and fuel could then escape. This, in turn, would result in a risk of fire or explosion as the fuel may contact hot parts of the vehicle, such as the exhaust system. According to the prior art, it is therefore known in practice to avoid this problem by providing a safety line which extends from the fuel filter, for example, to an activated charcoal filter. However, because of the additional parts and the need for mounting this line, this constitutes a problematic and expensive and therefore technically unsatisfactory solution.
In DE 43 21 927 A1, a filter unit which can be pressurized and has a degassing nozzle is described, in which the degassing nozzle is separated from the housing compartment by a gas-permeable filter.
However, this filter unit is not suitable for use in internal combustion engines since it would not withstand the high pressures which may occur in them. Moreover, in the filter unit described in this publication, the cartridge-like filter element and the degassing opening are very disadvantageous because they are of a complicated design and it is difficult to operate them.
A venting device in a fuel system is also known from DE 37 31 206 C2, which device is intended to insure reliable venting without overflow of fuel during the operation of an internal combustion engine. This is achieved by the special design of a valve seat which, while being gas permeable, is supposed to be largely liquid-tight.
However, the non-return valve described therein does not operate at low pressures, and therefore requires a high pressure on the venting device. Consequently, he venting device is not suitable for low pressures operation.
It is therefore the principal object of the invention to provide a satisfactory solution for the problems referred to above which, at the same time, safely prevents any escape of fuel at the venting nozzle of the fuel filter and the risk of fire or explosion generated thereby.